The advent of microelectromechanical systems (MEMS) processing techniques has enabled the fabrication of small, high-performance sensors such as accelerometers and gyroscopes. One particularly useful MEMS sensor is the tuning fork gyroscope, which is utilized to sense angular rate, i.e., angular velocity (and hence, angular displacement) in a variety of applications. A conventional tuning fork gyroscope includes one or two proof masses suspended above a substrate, typically suspended above the substrate by suspension beams that allow the proof masses to vibrate freely. The edges of the proof masses include electrode fingers, or “combs.” Between and to either side of the proof masses is drive circuitry with complementary sets of combs interleaved with the proof mass combs. Voltage applied between the interleaved sets of combs enables the vibration of the proof masses in the plane of the substrate surface. To facilitate fabrication of the gyroscope, i.e., a “comb drive” device, the proof masses, suspension beams, and both sets of interleaved combs typically have the same thickness (typically approximately 20 micrometers (μm), e.g., 23 μm).
When the gyroscope rotates (undergoes angular motion), sense plates below the proof masses detect differential vertical displacement thereof (e.g., by measuring capacitance between the proof masses and the sense plates). This differential vertical displacement is translated directly into a measure of angular rate by the gyroscope. However, the performance of conventional tuning fork gyroscopes for various applications is often limited. For example, the wide-bandwidth rate noise, or “angle random walk,” often may be limited to values of 0.1°/h1/2 or higher. Moreover, bias error over temperature may be limited to values of 10°/h or higher for conventional tuning fork gyroscopes.
Thus, in order to service the demand for higher-performance sensors incorporating comb drives and proof masses (such as tuning fork gyroscopes), improved designs and methods for constructing such sensors are needed.